The present invention relates to fluid pumps and particularly a fluid pump with means for separating gas from the fluid being pumped.
In fluid pumps and particularly in gasoline pumps, gas or air leaks on the inlet side of the pump causes air to mix with the liquid output of the pump which then is less than the metered amount. This is a particularly troublesome problem in the gasoline dispensing art where the consumer is paying for gasoline and regulations require the amount of air in the pumped gasoline to be held to a minimum so that the consumer receives relatively pure gasoline for the metered amount of gasoline pumped. As the price of gasoline increases, the desirability of eliminating metering error from the fuel dispensed naturally increases.
In U.S. Pat. No. 3,715,863, issued to P. Zanoni on Feb. 13, 1973, and assigned to the present assignee, a gasoline pump is disclosed which has heretofore provided an adequate solution to the air problems associated with gasoline pumps. With such apparatus, however, it is still possible for an amount of up to 4 percent of air to gasoline by volume mixture to still be pumped through the system. In many markets, the air must be less than 0.5 percent of the output mixture and such improved performance naturally is desirable in all markets in any pump operation.
In gasoline pumps, the air removal efficiency is measured by providing a series of test orifices, on the pump inlet to admit air to the gasoline inlet. These orifices range in size from 0.1 millimeter and increase in increments of 0.1 millimeter until the point is reached where the pump breaks suction stopping the delivery of product. With a test orifice of 1.2 millimeters, the air bubble cone in the cyclone separating chamber of the prior art pump represented by U.S. Pat. No. 3,715,863 becomes larger in diameter than the scavenging tube thereby bypassing the separating chamber and mixing with the gasoline at the outlet which results in a metering error of approximately 4 percent. If the scavenger tube and orifice is increased in diameter without other pump modifications, the scavenger tube also admits an increased flow rate of entrained gasoline which enters the ventilating chamber and must be returned to the pump inlet. Thus, for example, by increasing the diameter of the scavenging tube from 1/2 to 3/4 inches in diameter, and the 0.089 orifice to 0.150 inches, it was found that the flow rate of gasoline into the vent chamber increases from one gallon per minute to 2.5 gallons per minute. This causes gasoline to be dispelled from the air vent since the float valve incorporated in the prior art device is unable to handle the additional bypass gasoline. In addition, it was discovered that the control valve at the outlet of the pump pulsates or hunts for an equilibrium position with the nozzle in the full open position. This is due in part to the air expanding at the outlet reducing the pressure against the valve until the spring counter-pressure closes the valve which cycle repeats causing valve chattering.
If the air allowed to enter the inlet side of the pump through a test orifice of 1.2 millimeters in diameter or larger such as occurs in the field when an air leak exists in the input pipe leading from the storage tank to the pump, the cyclone separator air bubble cone naturally increases to a size which is not effectively captured by the relatively small diameter scavenging tube and the control valve hunting becomes markedly increased greatly decreasing the efficiency of operation of the pump and introducing a greater amount of air to the fuel mixture at the outlet of the pump.
In order to provide a pump, therefore, with improved air elimination performance under almost unlimited air conditions, the interrelated scavenging tube, float valve, and control valve criteria must be taken into account to provide improved performance possible with the pump of the present invention.